U.S. officials and high-tech business giants have launched an assault against what they view as a massive threat to the Internet and to Silicon Valley’s bottom lines: foreign governments.

In a congressional hearing Thursday, they will warn lawmakers of a growing movement led by China, Russia and some Arab states to hand more control of the Web to the United Nations and place rules on the Internet that the U.S. companies say would empower governments to clamp down on civil rights and free speech.

That could mean the Web might look drastically different in other countries than it does in the United States, opponents of the proposals say. An Internet user in Uzbekistan could be more easily tracked by government officials and might get access to only a portion of the Google search results seen in the United States, for example.

In a rare coordinated effort to knock down the proposals, Google, Microsoft, Verizon and Cisco also warn of financial risks to their businesses if new rules are adopted. They say some nations may push forlaws on Internet firms that could lead to tariffs on Internet service providers such as Verizon, or even Web firms such as Facebook that enable people to communicate over the Internet.